1. Field of the Invention
This invention relates to a machine element with a multiple screw action for converting rotary movement into straight line reciprocation, the element being constructed of identical segments. It also relates to means and methods of providing such a structure from identical molded segments which are stacked together and to the details of such identical segments. Finally, it relates to devices utilizing a reversing lead screw constructed in this manner, such as a scraping device utilized with a roll in an electrophotographic copying device, for example.
2. Description of the Prior Art
Reversing lead screws are known in the art and have been utilized in various mechanisms to transform rotary movement into straight line reciprocation. For example, U.S. Pat. No. 2,193,394 discloses the use of such a mechanism in a gear-shaft pump. This patent gives no details of construction or method of making the reversing lead screw, which it refers to as a "shaft having oppositely-spiraled thread grooves", although the shaft appears to be formed of a continuous solid element. U.S. Pat. No. 3,048,054 is of interest as disclosing a guide roller in which a twin groove defines a central narrow bar or rib. The roller consisits of one left-hand and one right-hand spiral rib arranged on the surface of the roller, meeting at the ends of the roller, and repeatedly crossing each other on the path between the ends of the roller to provide a reversing lead screw. This reference suggests that the grooves or ribs defining these paths be provided by milling what appears to be a solid, continuous shaft. However, it is of interest to note that the end portions of the roller which provide reversing action to the follower element which rides on the rib is taught to be detachably secured to the roller.
Design News of Apr. 7, 1975 discloses a reversing machine tool carriage for use with a proprietary "Rollnut Reverser". Again, the threaded shaft appears to be a continous, solid element. IBM Technical Disclosure Bulletin Vol. 18, No. 2, July 1975, at pages 326-327 discloses a scraper for a roll, the scraper riding on a solid reversing lead screw. The present invention makes possible the provision of such a scraper utilizing a reversing lead screw constructed from identical half-pitch double helix segments. An auger composed of a number of identical, full pitch single helix rib segments mounted on a rigid shaft is known to exist. This latter reference does not disclose the molding of a double helix, nor the provision of a reversing lead screw comprised of identical molded double helix segments.
It will be noted that in none of the prior art is a double helix reversing lead screw provided in which the body of the lead screw consists of a number of identical half-pitch molded segments. Additionally, no reference discloses how a reversing lead screw of indefinite length can be constructed from a plurality of identical half-pitch molded segments. No known reference discloses how inexpensive small, half pitch, hollow, molded segments can be utilized to provide an inexpensive lead screw of any length. Finally, no such reference discloses the use of such a segmented lead screw with a roll scraper.
Therefore, one important object of this invention is to provide a reversing lead screw consisting of a number of identical molded segments.
Another important object of this invention is to provide a double helix reversing lead screw consisting of a number of identical segments, in which no segment provides more than one-half pitch of any guideway.
Yet another object of this invention is to provide a reversing lead screw consisting of a plurality of identical segments and in which such segments can be replaced, added, or removed to repair damage or to change the length of the screw.
Still another object of this invention is to utilize small, identical molded segments to provide an inexpensive reversing lead screw of any length.
Another object is to provide the ability to manufacture complex parts from small, identical molded segments and the ability to manufacture such identical segments.
Another object is to avoid expensive machining operations involved in making this type of complex parts out of solid stock.
An additional object of this invention is the provision of a roll scraper mounted on a reversing lead screw constructed of identical segments.